When introducing a new Exchange Server into your existing Exchange environment, the installer may throw the error “Database is mandatory on UserMailbox” and prevent you from continuing.
If you examine the Exchange Setup Logs (which can be found at “C:\ExchangeSetupLogs\ExchangeSetup.txt”) you may find a few more clues as to which mailboxes are missing their databases parameter.
Towards the end of our Exchange setup log, we found the following two error lines.
[07/01/2020] [1] [ERROR] Database is mandatory on UserMailbox. [07/01/2020] [1] [ERROR-REFERENCE] Id=SystemAttendantDependent___04cc4eded45c32a6bf14ee3fe543df60 Component=EXCHANGE14:\Current\Release\PIM Storage\Discovery
The key here is “SystemAttendant.” The System Attendant is an arbitration mailbox. Let’s check on the health of all our arbitration mailboxes. We can do this by entering the following command into the Exchange Management Shell.
C:\> Get-Mailbox -Arbitration | Select Name | Format-Table Name ---- SystemMailbox{bb558c35-97f1-4cb9-8ff7-d53741dc928c} FederatedEmail.4c1f4d8b-8179-4148-93bf-00a95fa1e042 SystemMailbox{1f05a927-7f83-496b-a118-a96cdde1cd3c} WARNING: The object SKARO.LOCAL/Users/SystemMailbox{1f05a927-7f83-496b-a118-a96cdde1cd3c} has been corrupted, and it's in an inconsistent state. The following validation errors happened: WARNING: Database is mandatory on UserMailbox. WARNING: Database is mandatory on UserMailbox. SystemMailbox{e0dc1c29-89c3-4034-b678-e6c29d823ed9} SystemMailbox{D0E409A0-AF9B-4720-92FE-AAC869B0D201} Migration.8f3e7716-2011-43e4-96b1-aba62d229136 SystemMailbox{2CE34405-31BE-455D-89D7-A7C7DA7A0DAA}
The output from this command identifies that we have a single broken system mailbox.
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